void Add(int addend1[], int addend2[], int sum[],
      int max_digit) {
   int carry = 0;
   for (int digit = 0; digit < max_digit; digit++) {
      temp = addend1[digit] + addend2[digit] + carry;
      sum[digit] = temp % 10;
      carry = temp/10;
   }
   sum[max_digit] = carry;
}
